Physics - Journal Articleshttp://hdl.handle.net/10468/2252018-02-22T06:34:27Z2018-02-22T06:34:27ZThree-dimensional self-assembled columnar arrays of AlInP quantum wires for polarized micron-sized amber light emitting diodesPescaglini, AndreaGocalińska, Agnieszka M.Bogusevschi, SilviuMoroni, Stefano T.Juska, GediminasMura, Enrica E.Justice, JohnCorbett, Brian M.O'Reilly, Eoin P.Pelucchi, Emanuelehttp://hdl.handle.net/10468/53572018-01-31T19:00:48Z2018-01-20T00:00:00ZThree-dimensional self-assembled columnar arrays of AlInP quantum wires for polarized micron-sized amber light emitting diodes
Pescaglini, Andrea; Gocalińska, Agnieszka M.; Bogusevschi, Silviu; Moroni, Stefano T.; Juska, Gediminas; Mura, Enrica E.; Justice, John; Corbett, Brian M.; O'Reilly, Eoin P.; Pelucchi, Emanuele
A three-dimensional ordered and self-organized semiconductor system emitting highly-polarized light in the yellow-orange visible range (580-650 nm) is presented, comprising self-assembled in-plane AlInP wires vertically stacked in regularly-spaced columns. More than 200 wires per column without detectable defect formation could be stacked. Theoretical simulations and temperature-dependent photoluminescence provided a benchmark to engineer multilayered structures showing internal quantum efficiency at room temperature larger than comparable quantum wells emitting at similar wavelengths. Finally, proof-of-concept light emitting diodes (LED) showed a high degree of light polarization and lower surface parasitic currents than comparable quantum well LEDs, providing an interesting perspective for high-efficiency polarized yellow-orange light emitting devices.
2018-01-20T00:00:00ZObservational signatures of mass-loading in jets launched by rotating black holesO'Riordan, MichaelPe'er, AsafMcKinney, Jonathan C.http://hdl.handle.net/10468/54292018-02-09T12:00:55Z2018-01-01T00:00:00ZObservational signatures of mass-loading in jets launched by rotating black holes
O'Riordan, Michael; Pe'er, Asaf; McKinney, Jonathan C.
It is widely believed that relativistic jets in X-ray binaries (XRBs) and active-galactic nuclei are powered by the rotational energy of black holes. This idea is supported by general-relativistic magnetohydrodynamic (GRMHD) simulations of accreting black holes, which demonstrate efficient energy extraction via the Blandford–Znajek mechanism. However, due to uncertainties in the physics of mass loading, and the failure of GRMHD numerical schemes in the highly magnetized funnel region, the matter content of the jet remains poorly constrained. We investigate the observational signatures of mass loading in the funnel by performing general-relativistic radiative transfer calculations on a range of 3D GRMHD simulations of accreting black holes. We find significant observational differences between cases in which the funnel is empty and cases where the funnel is filled with plasma, particularly in the optical and X-ray bands. In the context of Sgr A*, current spectral data constrains the jet filling only if the black hole is rapidly rotating with a gsim 0.9. In this case, the limits on the infrared flux disfavor a strong contribution from material in the funnel. We comment on the implications of our models for interpreting future Event Horizon Telescope observations. We also scale our models to stellar-mass black holes, and discuss their applicability to the low-luminosity state in XRBs.
2018-01-01T00:00:00ZDetermining the jet poloidal B field and black-hole rotation directions in AGNsGabuzda, Denisehttp://hdl.handle.net/10468/55012018-02-21T12:01:24Z2018-01-01T00:00:00ZDetermining the jet poloidal B field and black-hole rotation directions in AGNs
Gabuzda, Denise
It is theoretically expected that active galactic nucleus (AGN) jets should carry helical magnetic (B) fields, which arise due to the rotation of the central black hole and accretion disk combined with the jet outflow. The direction of the toroidal component of the helical B field Bφ is determined by the direction of the poloidal component Bp of the initial seed field that is “wound up” and the direction of rotation of the central black hole and accretion disk. The presence of the jet’s helical B field can be manifest both through the presence of Faraday rotation gradients across the jet, and the presence of appreciable circular polarization, which comes about when linearly polarized emission from the far side of the jet is partially converted to circularly polarized emission as it passes through the magnetized plasma at the front side of the jet on its way towards the observer. When both of these properties are manifest, they can be used jointly with the jet linear polarization structure to uniquely determine both the direction of Bp and the direction of the central rotation. This technique has been applied to 12 AGNs. The results indicate statistically equal numbers of outward and inward Bp and of clockwise (CW) and counter-clockwise (CCW) rotations of the central black holes on the sky. However, they suggest that the directions of Bp and of the central rotation are coupled: CW/CCW central rotation is preferentially associated with inward/outward poloidal B field. This leads to a preferred orientation for the toroidal B-field component corresponding to inward current along the jet
2018-01-01T00:00:00ZAn integration-friendly regrowth-free tunable laserCaro, LudovicDernaika, MohamadKelly, Niall P.Morrissey, Padraic E.Alexander, Justin E.Peters, Frank H.http://hdl.handle.net/10468/52652018-01-10T19:00:56Z2017-12-11T00:00:00ZAn integration-friendly regrowth-free tunable laser
Caro, Ludovic; Dernaika, Mohamad; Kelly, Niall P.; Morrissey, Padraic E.; Alexander, Justin E.; Peters, Frank H.
This paper presents a single-mode tunable laser operating in the L band. The facetless design, along with a regrowth-free fabrication that does not require high-resolution lithography techniques, contribute to make the laser a suitable candidate for monolithic integration with other components. Vernier tuning is demonstrated over a range of 47nm, with sidemode suppression ratio (SMSR) values over 30dB and a linewidth of 800kHz.
2017-12-11T00:00:00Z